I've just finished my decking ready for the summer, but now the sun has come out I've noticed the boards are starting to arch and warp in the heat. My decking design also includes some planters that are constructed using horizontal decking boards for the sides which are skew srewed from the back onto a frame and the warping is pulling the screws out!

Has anyone got any nifty tricks how I can stop this warping from happening? I wanna get a least one BBQ out of it before my decking pulls itself apart!!

If anything, I have over engineered the support frames under the decking. All support joists are no more than 400mm apart and are mounted on a double joisted sub frame with concreted support posts every 800mm. You could probably park a car on it and it wouldn't budge!

The board themselves were from a decent timber merchant. As I wanted the decking to last I avoided the kind of decking you get from B&Q and such like. The odd thing is that the wood was all delivered last August 2009 so plenty of time to weather the boards.

The main floor area of the decking was actually completely at the end of September 2009 but it's only been the last couple of weeks since the sun has come out that this 'cupping' has occurred.

The length of the longest boards are 4000mm end to end. They are 28mm thick so used 60mm long decking screws and screwed two into each joints about 20mm or so from the edge of the boards.

I did notice that they had flattened slightly yesterday evening after they had been rained on a bit and cooled so had the opportunity to re-tighten the screws I'd put in.

I think part of the problem was that I didn't want to over tighten the screws in the first place. I tightened them level with just under the surface of the boards which may have allowed them more movement.

I'm still a bit nervous that when the sun pops out again it'll do the same and pull the screws through even deeper.

hello, warping, cupping surface cracks, all are the result of a deck that has too much moisture in it compared to its surroundings. If you want your wood to be stable, its MC (moisture content) should be IN BALANCE with its environment. If not, then it starts to work such as warping and cupping. The remedies are:1) go back to your supplier and see what is their sales promiss (did they say dried deck?)2) cut the boards into two pieces and flap them over3) next time: buy thicker boards, and/ or narrower boards, the board itself has then more power to resist its own forces. 4) you can drill deepeer and put in bigger screws, you will hld on for some more time but eventually the wood will be stronger and pups out.

deck cupping due to inbalance of moisture content between the board and its surrounding

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deck cupping due to inbalance of moisture content between the board and its surrounding

What screw length, and are the holes oversized around the shanks to allow for widthways movement.

Generally yes you should screw them down tight, and tighten the fixings as necessary, but the answers to the above questions will help just in case.

1) go back to your supplier and see what is their sales promiss (did they say dried deck?)

More specifically ask them for a moisture content, dried would encompass air dried (20ish%) or kiln dried to a specific level, normally 16% for external decking. I suspect you possibly have a tropical hardwood, and some suppliers provide them poorly air dried.

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